In addition to wireless end devices that are used in wireless systems to transmit mobile telecommunications data, for example AMPS (Advanced Mobile Phone System), GSM (Global System Mobile) and PCS (Personal Communication System), end devices are being developed that also fulfill additional functionalities, such as location determination (GPS=Global Positioning System), wireless connection to EDP devices (Bluetooth), or to a local network (WLAN=Wireless Local Area Network).
An aerial switch can switch between various frequency bands in time slots (time division), wherein a common send/receive antenna is connected sequentially with various signal paths. This solution has the disadvantage that the respective signal path is not, at any time, available for data transmission.
With a common antenna, signals that are to be transmitted from various wireless systems can be separated from one another (frequency division) with a diplexer that comprises a low pass filter and a high pass filter. The send or receive signal of the same wireless systems is rerouted, for example, by a duplexer in the corresponding send or receive path.
In the case of an end device having multiple functionalities, each functionality generally is assigned to a specific frequency range for data transmission.
For example, end devices with two antennas are known, wherein one antenna is used to transmit in the PCS band and the other antenna is used to transmit Bluetooth, WLAN or GPS data. The solution using separate antennas has the advantage of especially high suppression of the counter-band and low insertion loss in both transmission ranges, but needs more space and/or costs more.
For example, it is possible to link the two signal paths, each signal path for one wireless system, wherein one signal path is for GPS data transmission with one send/receive antenna via an antenna duplexer that has a low pass filter, a high pass filter and a band pass filter provided for GPS data transmission which switches all signal paths parallel to an antenna. The solution using one antenna saves space, but incurs high insertion loss because one part of the wanted signal gets lost by the antenna-side branch of the signal path.
A diplexer on the antenna side can be used to separate, for example, AMPS and PCS signals for a multiband end device with GPS functionality, wherein a GPS signal path in accordance with the diplexer is rerouted, for example, with a band pass filter or an additional output-side diplexer.
All previously known end devices having an antenna and several functionalities, i.e., with multiple signal paths each attached to an antenna connection and being parallel to one another, are characterized by high insertion loss.
The task is therefore to provide a front-end circuit that can be operated with only one antenna that, first, separates signals in the case of multiple functionalities and, second, has low insertion loss in the transmission range of at least one signal path.